I mentioned this art installation to a coworker who is in a knitting group. She responded that her circle wouldn't do something like this; they would (and have) knit sweaters for homeless people. The bridge really didn't need a sweater.

Your coworker's group's behavior is commendable. It would be nice to see more initiatives like that.

That said, it is possible to knit a "sweater" for a bridge AND for the homeless, and even if it weren't, not everyone has to be doing something to help the homeless every waking minute of their day, so it's kind of a weird criticism. Unfortunately, we live in a culture where people regularly throw out leftovers instead of saving them to give to the homeless members of their community. Many more pass the homeless by without making eye contact or even thinking about it. The neglect of homeless people is a major issue... but I don't see why this specific decoration is relevant. Plenty of people knit for themselves or for their friends rather than for the homeless, but it would be foolish to criticize all of them.

It may not be to everyone's taste, but public art is good for communities. It adds something interesting to the bridge and it gets people to stop and become aware of the place they are. It also gives them something to think about-- as demonstrated by this conversation! :)